Teardown and rebuild procedure

Could someone please confirm what is needed to get the system to work once it has been torn down and completely removed from the case? I am trying to get it to boot with just the motherboard and the essential components however I gathered that some other parts required:

When I first tore down the system I ran both the CPU and GPU without their heatsinks (whoops, rookie error ) however I hope the broken hamburg cables were preventing them from microwaving themselves. There was also a high pitch whining sound coming from the mobo, is that normal?

Its very unsettling when you've taken it all apart and now trying to see if it works again!